Stereoscopic Vision
FIG. 1 illustrates stereoscopic vision. Humans have two eyes, a left eye 110 and a right eye 120 separated by a horizontal distance. As a consequence of this separation, the two images that are projected onto the retinas of these eyes are slightly different, depending on the arrangement of elements in a scene being viewed. Image plane 130 depicts the two different image projections 140. If two objects, element A 160 and element B 170 are located at different depths 150 to an observer, then the horizontal separation of corresponding object points, known as disparity, varies with depth 150. The human brain is able to interpret the inverse of this process. By analyzing the disparity of corresponding object points in the images of the left eye 110 and right eye 120, the brain is able to fuse these images into a single coherent 3D scene with objects at different depths.
Stereoscopic Imagery
Despite being almost as old as photography itself, stereoscopic imagery is only recently being commoditized at a large scale. For example, stereoscopic movies are being produced and released, and stereo capture systems (such as video and still cameras) are becoming available for consumers. Such movies are commonly referred to by producers as “3D.” While these systems allow capturing of the real world with stereoscopic image pairs, they do not provide opportunity for stereoscopic art creation, such as sketching, painting, or drawing.
Compared to monoscopic artwork, which only requires a single view, stereoscopic artwork requires two views, or one view along with depth information so that the disparities for the second view can be computed from that information. A problem of stereoscopic art creation can therefore be stated as the problem of creating some artwork plus depth information.
Creation of stereo artwork (e.g. paintings, sketches, etc.) is difficult due to the necessity for stereo-consistent disparity information of the stereo pair. In the past, mechanical drawing devices have been designed that facilitate stereo sketching. However these mechanical drawing devices are complex to build and difficult to operate, as the user is required to draw free-hand in space. Furthermore, while such devices have been used to create some original stereoscopic artwork, there are several limitations associated with such physical devices, such as the volume covered by a device is spatially limited, physical marking devices cannot be guaranteed to be sufficiently similar to fuse two images into a stereographic image, and drawing implements are difficult to position in three dimensions.
Digital drawing techniques have been developed for generating a valid stereoscopic image pair. One such digital drawing technique is painting depth onto a 2D canvas. Given a digital painting, a user draws a corresponding depth image, where grayscale values correspond to depth values (e.g., lighter being closer to the viewer, and darker being further away). However, this technique includes the necessity of drawing an appropriate depth image, which is difficult, specifying absolute and relative values, accounting for occlusion boundaries, and drawing on a non-stereoscopic image. Another digital drawing technique is directly on a digital three-dimensional model. This approach requires a three-dimensional model of the scene to first be created, which can then be painted with different colors. As the step of creating such a three-dimensional scene can often be as or more time-consuming than creating a painting, this approach may generally be too time expensive for practical applications.